SAN FRANCISCO -- Buster Posey and Kelby Tomlinson contributed RBI doubles to a two-run, tiebreaking seventh inning, and five San Francisco Giants pitchers combined on a five-hitter Wednesday night, leading the defending World Series champions to a 4-2 victory over the Chicago Cubs.

In snapping a five-game losing streak to the Cubs, the Giants (67-59) kept pace with the National League West-leading Los Angeles Dodgers (69-56), who won earlier in the evening at Cincinnati. The Dodgers' lead over the Giants remains 2 1/2 games.

The Cubs (73-52) lost for just the sixth time in their past 21 road games. They also lost ground to both the first-place St. Louis Cardinals (81-45) and wild-card-leading Pittsburgh Pirates (76-49) in the NL Central.

After each team got two runs in the first inning, the score remained 2-2 into the pivotal sixth inning.

Giants first baseman Brandon Belt tripled past diving center fielder Chris Denorfia in to begin the rally.

Posey followed with just his third hit in 22 at-bats, a double to right-center field off Cubs starter Kyle Hendricks that scored Belt with the eventual game-winning run.

One out later, Tomlinson improved to 5-for-14 (.357) with runners in scoring position in his brief Giants career, slicing a double to right field that plated Posey to make it 4-2.

The Cubs, who had won six in a row, threatened to get even in the seventh when Giants left fielder Nori Aoki misplayed pinch hitter Tommy La Stella's line drive into a two-base error, putting the potential tying runs in scoring position with just one out.

Right-hander Hunter Strickland replaced starter Jake Peavy and struck out Cubs shortstop Addison Russell for the second out, and lefty Javier Lopez came on to whiff left fielder Kyle Schwarber to end the threat and retain the two-run cushion.

Right-hander Sergio Romo worked a 1-2-3 eighth inning to set the stage for closer Santiago Casilla, who recorded his 31st save by striking out two of the three Cubs he faced in the ninth.

Peavy (4-6) got the win, the fourth in his past six decisions. He allowed two runs on five hits in his 6 1/3 innings, walking three and striking out three.

The four Giants relievers combined for 2 2/3 innings of perfect relief, striking out four.

Hendricks (6-6) took the loss, his first since July 22. He gave up all four Giants runs on five hits and three walks. He struck out six.

Four of the Giants' five hits against Hendricks went for extra bases, including Aoki's leadoff home run in the first inning. The homer was his fifth of the season and second as the Giants' first batter of the game.

Belt had two of the Giants' six hits.

Schwarber and third baseman Kris Bryant, both of whom doubled in Chicago's two-run first, had two hits apiece for the Cubs.

Both teams scored two runs in the first inning, each taking advantage of an unusual occurrence to make it happen.

Bryant got the Cubs on the board first with a two-out, two-run single that scored Schwarber and right fielder Chris Coghlan.

The inning would have been over earlier if not for the fact that Peavy and Posey ran together on Schwarber's game-opening popup in front of the mound. The ball fell untouched as Schwarber hustled into second base, credited with a double.

Aoki got one of those runs back on Hendricks' second pitch, and the Giants then loaded the bases with two outs on three walks.

Hendricks appeared to get out of the jam when he got center fielder Juan Perez to ground to shortstop, but the Tomlinson outran Addison Russell's routine throw to second base, allowing right fielder Marlon Byrd to score the tying run.

NOTES: Cubs LF Kyle Schwarber batted leadoff for the first time this season, replacing CF Dexter Fowler, who was out of the starting lineup because of hand and shin injuries. ... Fowler's injuries were the result of getting hit on the hand by a pitch Monday and fouling a ball off his shin Tuesday. ... Chicago C David Ross returned home and was placed on the family medical emergency list. OF Matt Szczur was recalled from Triple-A Iowa. ... SS Brandon Crawford (left oblique tightness) and OF Gregor Blanco (strained left hip) were not in the Giants' starting lineup. ... San Francisco manager Bruce Bochy indicated before the game that RHP Matt Cain is not a sure thing to retain his spot in the rotation when it comes up again Sunday against St. Louis. RHP Tim Hudson (strained right shoulder), who threw a bullpen session Wednesday, could be reinstated from the disabled list to start in Cain's place.